In 1976, Paul Petzoldt, a mountaineer and founder of the National Outdoor Leadership School, proposed a theory to help backpackers plan trips and calculate their energy needs while on the trail in his book, Teton Trails. As defined by Petzoldt's theory, one energy mile is equal to the energy required to walk one mile on flat terrain. He also said that you should add two energy miles for every 1000 feet of elevation gain. In other words, if you hiked 1 mile while climbing 1000 feet, you would've used the equivalent of three energy miles.
Petzoldt's theory, however, had never been tested before - that is until recently, when a study was conducted at Western Carolina University’s Exercise Physiology Laboratory, by Maridy Troy, assistant professor in WCU’s health and physical education program, and Maurice Phipps, professor of parks and recreation management.
The study measured the energy cost and perceived exertion for walking on flat terrain, with and without a backpack, as well as an elevation gain of 1000 feet. Results from the data show an average of a 1.6-mile equivalent for a 1000 foot gain in elevation. Differences between females and males ranged from 1.32 to 2.02. Professor Phipps stated in an article for WCU news that the range revealed by the study was due to the “hikers” personal weight differences. The abstract from the study states that further research using heavier expedition packs at higher altitudes could also reveal changes in energy cost.
“It is remarkable that Petzoldt’s energy mile theory is so close to the actual energy cost measured during our study,” Phipps stated.
Phipps also said the energy required for hiking up steep mountain trails would vary for individuals and groups, and the variables of the trail would also factor in, but he recommends that backpackers stick with Petzoldt’s theory of adding two energy miles for every 1,000 feet in elevation gain.
I found this information to be extremely interesting. Petzoldt’s theory happens to be the same formula that I use to calculate difficulty ratings for trails in the Smokies. I discovered the formula while visiting a website for trails in Colorado several years ago. The website stated that the equation was developed by Dick Holley, and came from Rocky Mountain National Park Dayhiker's Guide by Jerome Malitz. I guess we didn't follow the tree all the way to its roots!
Although the formula may not be exact, what Paul Petzoldt was essentially trying to solve was how many calories a hiker or backpacker burns while hiking. With today's internet technology that is much easier to do. The Hiking Dude has an excellent calorie calculator on his website. It takes into account your weight, plus the weight of you backpack, the distance you’ll be hiking, and how much elevation you’ll gain along the way. This can be useful in determining (roughly) how much food you’ll need to pack for a hike.
For more information on the study you can contact Professor Phipps at email@example.com.